1. Field of the Invention
The present invention is related to a coordinate reading apparatus and a coordinate indicator, in which a coordinate value of a desirable position on a tablet, indicated by the coordinate indicator, is calculated, and the calculated coordinate value is output.
2. Description of the Related Art
As a conventional coordinate reading apparatus, Japanese Laid-open Patent Application No. 2-249019 opened in 1990 describes a coordinate reading apparatus for calculating the coordinate value of a position indicated by a coordinate indicator, in which a resonant circuit is provided in the coordinate indicator, an AC magnetic field having a frequency nearly equal to the resonant frequency of the resonant circuit is applied from the tablet to the coordinate indicator, the signal reflected from the resonant circuit is received by the tablet, and thus the coordinate value of the indicated position is calculated in response to the received signal.
On the other hand, U.S. Pat. No. 5,532,598 discloses "AMORPHOUS METAL TAGGING SYSTEM FOR UNDERGROUND STRUCTURES INCLUDING ELONGATED PARTICLES OF AMORPHOUS METAL EMBEDDED IN NONMAGNETIC AND NONCONDUCTIVE MATERIAL" to Clark, Jr. et al. In this amorphous metal tagging system, the amorphous metal tag is attached to the object under examination, and this metal tag produces a reaction caused by the Barkhausen effect when the metal tag is located in the magnetic field. The circuit for generating the magnetic field, and also the circuit for detecting the reaction caused by the Barkhausen effect are provided in the detecting circuit. Then, existence of the object under examination is detected from the remote position.
For the sake of easy understanding of this metal tagging system, the abstract of U.S. Pat. No. 5,532,598 will now be described as follows:
An electromagnetic tagging system is provided for remotely detecting and locating polymeric and other non-conductive structures situated behind barriers, such as underground plastic pipes or containers. The system comprises a fluctuating magnetic field source, a pattern of tags embedded in discrete regions of the wall of the polymeric structure, each tag including an amorphous magnetic metal target for generating a Barkhausen response when exposed to the fluctuating magnetic field source, and a portable detection circuit movable along the ground or other control surface for remotely detecting the Barkhausen response. The amorphous magnetic material in each tag is preferably in the form of a plurality of elongated particles having aspect ratios of at least 3 to 1 and arranged end-to-end. The pattern that the tags are arranged in provide information concerning the identity, orientation, or extent of the structure, and the portable detection circuit is capable of detecting at least two of the tags simultaneously as it is moved over the surface of the ground so that the patterns of the tags may be easily determined.
The Barkhausen effect, or the Barkhausen response conducted in this metal tagging system will result in the below-mentioned phenomenon.
In the case that a ferromagnetic material has a uniform crystal structure, this ferromagnetic material has a linear magnetizing characteristic with respect to a continuous change in field strength of an external magnetic field. This is caused by the fact that when a magnetizing direction of internal magnetic domains and a magnitude of the internal magnetic domains are changed by the application of the external magnetic field, a magnetic domain wall which constitutes each of the magnetic domains can be freely moved in response to the field strength of the external magnetic field.
To the contrary, in such a case that a crystal structure of a ferromagnetic material is not uniform, or this ferromagnetic material has a portion whose magnetizing characteristics are partially different in response to the applied stress, the following phenomenon will occur. That is, the movement of the magnetic domain wall is disturbed in a discontinuous portion of the crystal structure. In this case, the magnetic domain wall is retained at this place until sufficient energy is given to this magnetic domain wall by the external magnetic field, and is rapidly moved to another place when sufficient energy is applied by which the magnetic domain wall comes out from this retained place. The Barkhausen effect imparts such a rapid magnetizing jumping phenomenon occurred in a ferromagnetic material having a magnetically unequal structure.
A ferromagnetic material with the Barkhausen effect represents a specific non-linear magnetizing characteristic. As a result, this ferromagnetic material may be used as such a functional element for generating a higher harmonic wave pulse field in response to the continuous change in the field strength of the external magnetic field. The Barkhausen response represents the higher harmonic wave pulse field produced by the magnetic material having the Barkhausen effect in this specification.
Also, there is a so-called "Large Barkhausen effect" phenomenon similar to the Barkhausen effect. The present invention is directed to an apparatus for using this Large Barkhausen effect. This Large Barkhausen effect will be explained more in detail later.
As previously described in the field of the coordinate reading apparatus, such a coordinate reading apparatus is known. That is, the coordinate value is calculated in response to the signal produced by coupling the tablet to the coordinate indicator by the resonant circuit. As to the field of detecting the presence of an article, the following apparatus is known. That is, the signal generated based on the Barkhausen effect is detected, and then the article is detected from the remote position.
However, in the above-described conventional coordinate reading apparatus, since a coil must be provided in the coordinate indicator, in the case that a stylus pen corresponding to a pen-shaped coordinate indicator is constituted, the pen tip cannot be made narrow. This is because the coil is required to be arranged in the pen tip. As a result, there is a problem in that the stylus pen cannot be easily utilized as a writing tool.
Although a passive type resonant circuit may be constructed, the coil and the capacitor should be electronically connected on the printed circuit board. There is another problem in that the resultant structure becomes complex. As a consequence, there is a further problem in that the width of the pen shaft cannot be narrowed.
In the above-described metal tagging system, the elongated amorphous metal is merely provided on the object under examination, so that the structure of the object under detection can be made simple. However, since this metal tagging system has not been constituted as a coordinate reading apparatus, there is the further problem that the precise position of the object under detection cannot be calculated. The coordinate reading apparatus is required to calculate the coordinate value of the position indicated by the coordinate indicator at a high resolution.